The present invention relates to multi-cylinder Diesel engines for motor-vehicles, in particular for trucks. The invention relates particularly, even if not exclusively, to engines of this type which are supercharged by means of a turbo-supercharger actuated by the exhaust gases.
In previous Italian patent application No. TO96A000327, which was still secret at the priority date of the present application, the Applicant has proposed a gasoline engine comprising:
at least one intake valve and at least one exhaust valve for each cylinder, each provided with respective spring means biassing the valve to a closed position, for controlling respective intake and exhaust conduits, a cam shaft, for actuating the intake and exhaust PA1 valves of the engine cylinders by means of respective tappets, each intake valve and each exhaust valve being driven by a cam of said cam shaft, PA1 each of said tappets being adapted to cause the respective intake or exhaust valve to open, against the action of said return spring means, by means of the interposition of hydraulic means including a chamber of fluid under pressure, PA1 the chamber of fluid under pressure associated with each intake or exhaust valve being adapted to be connected, by means of a solenoid valve, to an outlet channel, in order to uncouple the valve from the respective tappet and cause the valve to close rapidly under the action of the respective return spring means, PA1 electronic control means for controlling each solenoid valve, in order to vary the opening time and stroke of the respective intake or exhaust valve, as a function of one or more parameters of operation of the engine. PA1 each cam of the cam shaft has a profile such as to tend to cause the respective intake or exhaust valve controlled thereby to open not only during a conventional opening stage within a regular cycle of operation of the engine, but also at some additional stages of the cycle, PA1 and in that said electronic control means are adapted to cause each solenoid valve to open, so as to keep the respective intake or exhaust valve closed, during said conventional stage and/or during one or more of said additional stages during which the respective cam would tend to cause the valve to open, so that the engine can be selectively operated according to different modes of operation by controlling said solenoid valves.
The above described system provides a variable control on the opening of the intake and exhaust valves, without modifying the mechanical elements which control the valve movement. Indeed, whereas in a conventional timing system the movement of each intake or exhaust valve is univocally determined by the geometry of the mechanical elements which control the valve (cam, rocker arm, tappet), in the above described system the solenoid valve controlling the chamber under pressure associated with a given valve can be caused to open at any time which is desired so as to empty said chamber from the oil under pressure and cause the intake or exhaust valve to close rapidly, under the action of the respective return spring means, even during a stage in which the respective cam would tend to keep said valve opened.